/* Copyright 2012 The Netty Project
 * 
 * The Netty Project licenses this file to you under the Apache License, version 2.0 (the "License"); you may not use
 * this file except in compliance with the License. You may obtain a copy of the License at:
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
 * an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the
 * specific language governing permissions and limitations under the License. */
package io.netty.example.factorial;

import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.handler.codec.MessageToByteEncoder;

import java.math.BigInteger;

/**
 * Encodes a {@link Number} into the binary representation prepended with a magic number ('F' or 0x46) and a 32-bit
 * length prefix. For example, 42 will be encoded to { 'F', 0, 0, 0, 1, 42 }.
 */
public class NumberEncoder extends MessageToByteEncoder<Number> {

	@Override
	protected void encode(ChannelHandlerContext ctx, Number msg, ByteBuf out) {
		// Convert to a BigInteger first for easier implementation.
		BigInteger v;
		if (msg instanceof BigInteger) {
			v = (BigInteger) msg;
		} else {
			v = new BigInteger(String.valueOf(msg));
		}

		// Convert the number into a byte array.
		byte[] data = v.toByteArray();
		int dataLength = data.length;

		// Write a message.
		out.writeByte((byte) 'F'); // magic number
		out.writeInt(dataLength);  // data length
		out.writeBytes(data);      // data
	}
}
